1. Field of the Invention
This invention relates, in general, to spiral mineral concentrators and, more particularly, to troughs for such concentrators, and even more particularly to laminated troughs, bonded chemically, and the process for producing the same.
2. Description of the Prior Art
Spiral concentrators, having one or more helical troughs, are widely used for the separation and concentration of minerals of varying densities by a gravity wash, as typified by the separator of P. J. Giffard, U.S. Pat. No. 4,476,980. Spiral concentrators have been in use for mineral concentration since before 1900, and materials of construction have been wood, cast iron, rubber, and more recently, urethane elastomer. Urethane elastomer has the distinct advantage of being moldable in a single piece which eliminates the roughness and leakage at joint; is lighter in weight; is moldable in a wide variety of shapes and textures; and has excellent abrasion and corrosion resistance characteristics.
A serious problem with the ultimate abrasion resistant urethanes, however, is that they are too flexible in thin sections to maintain exacting shape control. One solution has been to make elastomer lined steel troughs for spiral concentrators. Another solution is to make fiberglass reinforced molded troughs by conventional spray or layup methods, demold, and then to coat the surface with a thin elastomeric sprayed coating. These products are heavy, expensive, and there is a tendency for delamination of urethane from dissimilar surfaces under humid heat ageing--a typical in-use environment. Further problems are that spray applications may yield uneven surface build-up; the fine detail of the mold being obscured, and there may be sufficient shrinkage of polyester type fiberglass systems to drastically change shape in a non-uniform manner during the curing cycle.